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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Theoretical Study of the Oxidation Mechanisms of Naphthalene Initiated by Hydroxyl Radicals: The OH-Addition Pathway
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Theoretical Study of the Oxidation Mechanisms of Naphthalene Initiated by Hydroxyl Radicals: The OH-Addition Pathway

机译：羟基自由基引发萘氧化机理的理论研究：OH加成途径

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The oxidation mechanisms of naphthalene by OH radicals under inert (He) conditions have been studied using density functional theory along with various exchange- correlation functionals. Comparison has been made with benchmark CBS-QB3 theoretical results. Kinetic rate constants were correspondingly estimated by means of transition state theory and statistical Rice-Ramsperger-Kassel-Marcus (RRKM) theory. Comparison with experiment confirms that, on the OH-addition reaction pathway leading to 1-naphthol, the first bimolecular reaction step has an effective negative activation energy around -1.5 kcal mol~(-1), whereas this step is characterized by an activation energy around 1 kcal mol~(-1) on the OH-addition reaction pathway leading to 2-naphthol. Effective rate constants have been calculated according to a steady state analysis upon a two-step model reaction mechanism. In line with experiment, the correspondingly obtained branching ratios indicate that, at temperatures lower than 410 K, the most abundant product resulting from the oxidation of naphthalene by OH radicals must be 1-naphthol. The regioselectivity of the OH.-addition onto naphthalene decreases with increasing temperatures and decreasing pressures. Because of slightly positive or even negative activation energies, the RRKM calculations demonstrate that the transition state approximation breaks down at ambient pressure (1 bar) for the first bimolecular reaction steps. Overwhelmingly high pressures, larger than 10~5 bar, would be required for restoring to some extent (within ~5% accuracy) the validity of this approximation for all the reaction channels that are involved in the OH-addition pathway. Analysis of the computed structures, bond orders, and free energy profiles demonstrate that all reaction steps involved in the oxidation of naphthalene by OH radicals satisfy Leffler-Hammond's principle. Nucleus independent chemical shift indices and natural bond orbital analysis also show that the computed activation and reaction energies are largely dictated by alterations of aromaticity, and, to a lesser extent, by anomeric and hyperconjugative effects.
机译：使用密度泛函理论以及各种交换相关泛函研究了惰性（He）条件下萘被OH自由基氧化的机理。已与基准CBS-QB3理论结果进行了比较。通过过渡态理论和统计莱斯-拉姆斯伯格-卡塞尔-马库斯（RRKM）理论相应地估算了动力学速率常数。与实验的比较证实，在导致1-萘酚的OH加成反应路径上，第一个双分子反应步骤的有效负活化能约为-1.5 kcal mol〜（-1），而该步骤的特征在于活化能OH加成反应途径中约1 kcal mol〜（-1）导致2-萘酚。根据两步模型反应机理的稳态分析，已经计算出有效的速率常数。与实验一致，相应获得的支化比表明，在低于410 K的温度下，由OH自由基氧化萘所产生的最丰富的产物必须是1-萘酚。随着温度升高和压力降低，在萘上的OH。加成物的区域选择性降低。由于活化能略微为正或什至为负，因此RRKM计算表明，在第一个双分子反应步骤中，过渡态近似值在环境压力（1 bar）下分解。要在某种程度上（大约5％的精度内）恢复近似值对所有与OH加成途径有关的反应通道的有效性，都需要大于10〜5 bar的压倒性高压。对计算的结构，键序和自由能曲线的分析表明，OH自由基氧化萘所涉及的所有反应步骤均符合Leffler-Hammond原理。原子核独立的化学位移指数和自然键轨道分析也表明，计算出的活化能和反应能在很大程度上取决于芳香性的改变，并在较小程度上受到端基异构体和超共轭作用的影响。

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